Pump, solvent effect

Among the best well-known examples of photostability after UV radiation, the ultrafast nonradiative decay observed in DNA/RNA nucleobases, has attracted most of the attention both from experimental and theoretical viewpoints [30], Since the quenched DNA fluorescence in nucleobase monomers at the room temperature was first reported [31] new advances have improved our knowledge on the dynamics of photoexcited DNA. Femtosecond pump-probe experiments in molecular beams have detected multi-exponential decay channels in the femtosecond (fs) and picosecond (ps) timescales for the isolated nucleobases [30, 32-34], The lack of strong solvent effects and similar ultrafast decays obtained for nucleosides and nucleotides suggest that ultrashort lifetimes of nucleobases are intrinsic molecular properties, intimately... 

The methodology for studying M-Ng complexes in the gas phase is essentially the same as the TRIR method for liquified noble gases a pump pulse photolyzes a metal carbonyl ion and the fragment is detected with the aid of a continuous IR laser. In these experiments helium is utilized as the standard buffer gas. A xenon complex may be detected by alteration in the spectrum and kinetics on addition of xenon. Since the spectra are free of solvent effects, the effect of coordination should be more easily discerned than in the liquid phase. This method has been used to study M(CO)sXe (M = Cr, Mo, W) and W(CO)sKr. Metal-xenon bond energies of ca. 35 kJmol are deduced from the kinetics of reaction with CO. The variation between metals in comparable to the error bars, about 4 kJ mol . The W-Kr bond energy is estimated to be less than 25 kJmol . ... 

Transient species are characterized by their spectra. If the spectra are not known, assignment can be made, for example, by comparison with analogues or from solvent effects. Reaction times are extracted from the analysis of AA(A, t) as a single exponential function of time or as the sum of exponential functions. If some reaction times are very close to the time-resolution of the set-up the analysis is made by fitting the convolution product ofthe pump-probe cross correlation function G t ) by a sum of exponential functions... 

Effect of acetonitrile in HPLC When the recovery of small molecules analyzed in serum is calculated based on the peak height of aqueous standards also treated by acetonitrile similar to serum, a high recovery is obtained. However, when the calculation is based on aqueous standards diluted in the mobile phase (pump solvent) a low recovery is obtained. In analyses of drugs in serum, acetonitrile in the sample decreases the peak height and limits the amount of sample to be injected on the column due to the formation of a short gradient leading to a non-symmetrical peak shape with a decrease in the plate number. Alternative deproteinizing mixtures for acetonitrile in HPLC have been proposed. 

When crystallisation is complete, the mixture of crystals and crude mother-liquor is filtered at the pump, again using a Buchner funnel and flask as described on p. 10, and the crystals remaining in the funnel are then pressed well down with a spatula whilst continual suction of the pump is applied, in order to drain the mother-liquor from the crystals as effectively as possible. If it has been found in the preliminary tests that the crystalline material is almost insoluble in the cold solvent, the crystals in the... 

Air. Biofilters are an effective way of dealing with air from industrial processes that use halogenated solvents such chloromethane, dichioromethane, chloroethane, 1,2-dichloroethane and vinyl chloride, that support aerobic growth (26). Both compost-based dry systems and trickling filter wet systems are in use. Similar filters could be incorporated into pump-and-treat operations. 

Temperature variation may also be a relevant factor in flowrate stability. Since the viscosity of the solvent is temperature dependent, wide swings in the ambient temperature can directly affect pump performance. The direct effects of temperature on pump performance usually are far smaller, however, than the effects on retention and selectivity therefore, control of column temperature is generally sufficient to obtain high reproducibility. 

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